[Studies on the regulation of steroid biosynthesis in the rat ovary]

The stimulatory effect of gonadotropins on steroid hormone production by the ovary is generally considered to be the result of an activation of the cholesterol side chain cleaving enzyme. The present study was undertaken to investigate whether the enzymic action of 3 beta-HSD and 20 alpha-HSD could be directly stimulated by hCG and/or PRL. Female immature rats were used. The ovaries were stimulated by PMSG injection to allow uniform growth of the follicles. The effect of hCG was evaluated both in in vivo and in vitro studies. The 3 beta-HSD activity in the ovarian tissue homogenate or dispersed cells was estimated from the rate of conversion of 14C-pregnenolone to 14C-progesterone in an in vitro incubation experiment. The activity of 20 alpha-HSD was measured by the conversion rate of 14C-progesterone to 14C-20 alpha-hydroxy-4-pregnen-3-one, hCG apparently stimulated the 3 beta-HSD activity both in vivo and in vitro. Under certain experimental conditions, PRL enhanced the stimulatory effect of hCG on 3 beta-HSD. Both hCG and PRL stimulated the 20 alpha-HSD activity. Intrinsic steroids, such as estrogens, androgens, and 20 alpha-hydroxy-4-pregnen-3-one, a major progestin in rodents, in the synthesis of steroid hormones was its inhibitory effect upon 3 beta-HSD.